JP2006069498A - Steering control system for front and rear wheels - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering control system for controlling the steered angle of a front wheel and the steered angle of a rear wheel, which system can stabilize the behavior of a vehicle in sudden slowing-down of the vehicle without causing the shift of a neutral point of the front wheel. <P>SOLUTION: A steering controller 3 carries out a deceleration control for steering the rear wheels 14, 14 in the same phase as the steered phase of the front wheels 11, 11 in the case of the sudden slowing-down when the deceleration A of the vehicle exceeds a threshold value A<SB>s</SB>of the deceleration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of front and rear wheel steering control devices that control a front wheel steering angle and a rear wheel steering angle.

In the conventional front and rear wheel steering control device, when the vehicle suddenly decelerates, the change in the vehicle speed sensor value input to the controller of the front wheel steering actuator is moderated to slow down the change speed of the front wheel rudder angle and suddenly change the vehicle behavior. (For example, refer to Patent Document 1).
JP 2001-270451 A

  However, in the above prior art, since the change in the front wheel steering angle is moderated during sudden deceleration, a neutral shift occurs between the steering steering angle and the front wheel steering angle after sudden deceleration. Therefore, a steering reaction force is generated when correcting this neutral deviation, which causes a problem that the driver feels uncomfortable.

  The present invention has been made by paying attention to the above-described problem, and the object of the present invention is to enable the front and rear wheels to stabilize the vehicle behavior without the neutral deviation of the front wheels when the vehicle is suddenly decelerated. The object is to provide a steering control device.

In order to achieve the above object, in the present invention,
Variable gear ratio control means for increasing the steering gear ratio, which is the ratio of the steering angle to the front wheel rudder angle as the vehicle speed increases;
Rear wheel steering control means for controlling the rear wheel steering angle according to the vehicle speed and the steering steering angle;
With
In the front and rear wheel steering control device for independently controlling the front wheel steering angle and the rear wheel steering angle,
A decelerating rear wheel rudder angle control means is provided for executing decelerating control to steer the rear wheel to the same phase as the front wheel when the vehicle deceleration is equal to or greater than the deceleration threshold value.

  In the present invention, when the vehicle is decelerating rapidly, the front wheels are steered in the direction of increasing the steering gear ratio according to the vehicle speed, while the rear wheels are controlled by the deceleration control. Since the vehicle is steered to the same phase as that of the vehicle, it is possible to suppress the vehicle steer characteristic from becoming an oversteer tendency without a neutral deviation when the front wheel steering is suppressed, and to stabilize the vehicle behavior. Further, since the rear wheel and the steering wheel are not mechanically connected, when correcting the rear wheel neutral deviation associated with the deceleration control, the driver does not feel uncomfortable due to the steering reaction force.

  Hereinafter, the best mode for carrying out the present invention will be described based on the first embodiment.

First, the configuration will be described.
FIG. 1 is an overall system diagram of the front and rear wheel steering control device according to the first embodiment.
A steering angle sensor 1 and a front wheel steering actuator 6 are provided on a column shaft 13 that connects a steering wheel 10 and a front wheel steering mechanism 12 that steers the front wheels 11 and 11.

  For example, the front wheel steering actuator 6 includes a motor and a speed reducer, and the output shaft of the motor is connected to the column shaft 13 via the speed reducer. The front wheel steering actuator 6 is a device that decelerates the rotation input via the column shaft 13 by the variable gear ratio according to the steering angle command value from the front wheel steering controller 4 and outputs it to the steering gear of the front wheel steering mechanism 12. As a result, the steering gear ratio, which is the ratio of the steering angle of the steering wheel 10 to the steering angle of the front wheels 11, 11, is variably controlled.

  Similar to the front wheel steering actuator 6, the rear wheel steering actuator 7 is composed of a motor, a speed reducer, and the like, and is output to the rack shaft of the rear wheel steering mechanism 15 for steering the rear wheels 14, 14 via the speed reducer. The shafts are connected. The rear wheel steering actuator 7 variably controls the steering angles of the rear wheels 14 and 14 based on the steering angle command value from the rear wheel steering controller 5.

  The front wheel steering controller 4 includes a target front wheel steering angle generated by the steering control controller (rear-wheel rear steering angle control means and steering gear ratio control means) 3 and an actual front wheel steering detected by the front wheel actual steering angle sensor 16. A steering angle command value that eliminates the deviation from the angle value is calculated, and the calculated steering angle command value is output to the front wheel steering actuator 6.

  The rear wheel steering controller (rear wheel steering control means) 5 is a deviation between the target rear wheel steering angle generated by the steering control controller 3 and the actual rear wheel steering angle value detected by the rear wheel actual steering angle sensor 17. Is calculated, and the calculated steering angle command value is output to the rear wheel steering actuator 7.

  The steering angle sensor 1 detects the steering angle of the steering wheel 10 using a pulse encoder or the like. The vehicle speed sensor 2 detects the vehicle speed from the average value of the wheel speeds.

  The steering control controller 3 generates a target front wheel steering angle and a target rear wheel steering angle according to the steering angle detected by the steering angle sensor 1 and the vehicle body speed detected by the vehicle speed sensor 2, and the target front wheel steering is generated. The angle is output to the front wheel steering controller 4, and the target rear wheel steering angle is output to the rear wheel steering controller 5.

  FIG. 2 is a control block diagram of the steering control controller 3, and the steering control controller 3 includes a target value generation unit 31 and a target output generation unit 32.

  The target value generator 31 generates a target yaw rate and a target lateral speed based on the steering angle from the steering angle sensor 1 and the vehicle body speed from the vehicle speed sensor 2. The generated target yaw rate and target lateral velocity are output to the target output generator 32.

  The target output generation unit 32 generates a target front wheel steering angle and a target rear wheel steering angle based on the target yaw rate and the target lateral speed from the target value generation unit 31.

  FIG. 3 is a control block diagram of the target value generation unit 31, and the target value generation unit 31 includes a vehicle model calculation unit 311 and a target value calculation unit 312.

  The vehicle model calculation unit 311 calculates vehicle parameters using a two-wheel model based on the steering angle and the vehicle body speed. The calculated vehicle parameter is output to the target value calculation unit 312. The target value calculation unit 312 determines the target yaw rate and the target lateral speed of the vehicle based on the steering angle, the vehicle body speed, and the vehicle parameters.

  FIG. 4 is a control block diagram of the target output generation unit 32. The target output generation unit 32 includes a target front and rear wheel steering angle calculation unit 321, a target front wheel steering angle difference value calculation unit 322, a gain calculation unit 323, A deceleration rear wheel steering angle calculation unit 324 and a deceleration control switching determination unit 325 are provided.

  The target front and rear wheel steering angle calculation unit 321 determines the target front wheel steering angle and the target rear wheel steering angle during normal control based on the target yaw rate and the target lateral speed. The determined target front wheel steering angle is output to the target front wheel steering angle difference value calculation unit 322 and the front wheel steering controller 4. Further, the determined target rear wheel steering angle during normal control is output to the rear wheel steering angle calculation unit 324 during deceleration.

  The target front wheel rudder angle difference value calculation unit 322 determines the target front wheel rudder angle difference value from the target front wheel rudder angle, and outputs it to the rear wheel rudder angle calculation unit 324 during deceleration.

  The gain calculation unit 323 determines the gain of the target rear wheel steering angle during deceleration with respect to the target front wheel steering angle difference value from the vehicle speed and a preset gain map (see FIG. 5), and the rear wheel steering angle calculation unit 324 during deceleration. Output to.

  The rear wheel rudder angle calculation unit 324 during deceleration determines the target rear wheel rudder angle during deceleration from the target front wheel rudder angle difference value and gain, and outputs the target rear wheel rudder angle during deceleration to the control switching determination unit 325 during deceleration.

  The deceleration control switching determination unit 325 determines a target rear wheel steering angle from the vehicle speed, the target rear wheel steering angle during normal control, and the target rear wheel steering angle during deceleration, and outputs the target rear wheel steering angle to the rear wheel steering controller 5.

Next, the operation will be described.
[Vehicle model calculation]
The vehicle model calculation unit 311 calculates vehicle parameters using the vehicle model shown below.

ここで、

である。 In general, assuming a two-wheel model, the yaw rate and lateral speed of the vehicle can be expressed by the following equation (1).

here,

It is.

When the transfer functions of the yaw rate and lateral velocity for the front wheel steering are obtained from the state equation, the following equations (3) and (4) are obtained.

ここで、

である。 The yaw rate transfer function is expressed by the following equation (5) from equation (3).

here,

It is.

ここで、

である。 Similarly, the lateral velocity transfer function is expressed by the following equation (7) from equation (4).

here,

It is.

が求められる。 From the above, vehicle parameters

Is required.

[Target value calculation]
The target value calculation unit 312 obtains a target yaw rate ψ ′ ^* and a target lateral velocity V _y ^* from the vehicle body speed V, the vehicle parameters, and a target value parameter described later.

The target yaw rate ψ ′ ^* is expressed by the following equation (9) from equation (5).

The target lateral velocity V _y ^* is expressed by the following equation (10) from equation (7).

ただし、yrate_gain_map，yrate_omegn_map，yrate_zeta_map，yrate_zero_mapはチューニングパラメータである。 Here, the parameter of the target yaw rate ψ ′ ^* is expressed by the following equation (11).

However, yrate_gain_map, yrate_omegn_map, yrate_zeta_map, and yrate_zero_map are tuning parameters.

ただし、vy_gain_map，vy_omegn_map，vy_zeta_map，vy_zero_mapはチューニングパラメータである。 Further, the parameter of the target lateral speed V _y ^* is expressed by the following equation (12).

However, vy_gain_map, vy_omegn_map, vy_zeta_map, and vy_zero_map are tuning parameters.

から、

[Target rudder angle calculation]
The target front and rear wheel steering angle calculation unit 321 calculates the target front wheel steering angle θ ^* and the target rear wheel steering angle δ ^* during normal control from the target yaw rate ψ ′ ^* and the target lateral velocity V _y ^* .

From

Accordingly, the target front wheel steering angle θ ^* and the target rear wheel steering angle δ ^* during normal control are expressed by the following equations (15) and (16).

[Target front wheel rudder angle difference value calculation]
The target front wheel steering angle difference value calculation unit 322 calculates the equivalent value θ _d ^* of the target front wheel steering angle during deceleration using the following equation (17) from the current target front wheel steering angle θ ^* . In addition, the equivalent value θ _d ^* of the target front wheel steering angle during deceleration is a value corresponding to the actual front wheel steering angle when performing control to match the target yaw rate only during front wheel steering during sudden deceleration.
θ _d ^* (s) = θ ^* (s) / (τs + 1) (17)
Here, τ is a time constant, and s is a Laplace operator.

A difference value Δθ ^* between the target front wheel steering angle θ ^* and the equivalent value θ _d ^* of the target front wheel steering angle during deceleration is calculated from the following equation (18).
Δθ ^* = θ ^* −θ _d ^* (18)

[Gain calculation]
The gain calculation unit 323 determines the gain B (V) from the vehicle speed V and a preset gain map (FIG. 5). As shown in FIG. 5, the gain B (v) is set so that the gain B (V) decreases as the vehicle speed V increases. The gain B (V) refers to the target rear wheel steering angle Δ ^* with respect to the target front wheel steering angle difference value Δθ ^* .

[Rear wheel steering angle calculation during deceleration]
The deceleration rear wheel rudder angle calculation unit 324 calculates the target rear wheel speed during deceleration using the following equation (19) from the target front wheel steering angle difference value Δθ ^* , the target rear wheel rudder angle δ ^* during normal control, and the gain B (v). The wheel steering angle δ _d ^* is calculated.
δ _d ^* = B (V) Δθ ^* + δ ^* (19)

[Deceleration control switching judgment]
The deceleration control switching determination unit 325 determines the target rear wheel steering angle δf ^* from the vehicle speed V, the normal control target rear wheel steering angle δ ^*, and the deceleration target rear wheel steering angle δ _d ^* .

First, the deceleration A is calculated from the vehicle speed V, the previous value _{Vb of the} vehicle speed, and the sampling time ΔT using the following equation (20). The deceleration A is positive.
A = (V _b −V) / ΔT (20)

Subsequently, the target rear wheel steering angle δf ^* is determined from the deceleration A. Here, the threshold value of the deceleration A and A _s. A _s is a deceleration at which a target front wheel steering angle difference value is generated so that the driver feels a front wheel cut.
When the deceleration is equal to or greater than the threshold value (A ≧ A _s ), the target rear wheel steering angle δ ^* is expressed by the following formula (21).
δf ^* = δ _d ^* (21)
At other times, the target rear wheel steering angle δ ^* is expressed by the following equation (22).
δf ^* = δ ^* (22)

[Back wheel neutral slip]
Stop from rapid deceleration of the vehicle, or by a decrease in deceleration, and the deceleration control to a target value of the target rear wheel steering angle [delta] _d ^* during deceleration, the normal control target value of the target rear wheel steering angle [delta] ^* When shifting to normal control, the neutral deviation is returned at a constant rear wheel steering angle return speed. At this time, since the neutral deviation is restored in accordance with the stop or the steering operation of the driver, it is difficult for the driver to feel uncomfortable.

If the return speed is defined as δ _A ′ and the previous value of the target rear wheel steering angle is defined as δf _i-1 ^* , the target rear wheel steering angle δf ^*
When δ ^* > δf ^*
δf ^* = δf _i-1 ^* + δ _A 'ΔT (23)
When δ ^* ≦ δf ^*
δf ^* = δf _i-1 ^* −δ _A 'ΔT (24)
If the target rear wheel rudder angle δf ^* and the target rear wheel rudder angle δ ^* during normal control become equal, normal control is resumed.

On the other hand, when sudden deceleration is started again when the rear wheel neutral slip is returned, the target rear wheel steering angle δf ^* must be returned to the target rear wheel steering angle δ _d ^* during deceleration. If the return speed is defined as δ _B 'and the previous value of the target rear wheel steering angle is defined as δf _i-1 ^* , the target rear wheel steering angle δf ^*
When δ _d ^* > δf ^*
δf ^* = δf _i-1 ^* + δ _B 'ΔT (25)
When δ _d ^* ≤ δf ^* ,
δf ^* = δf _i-1 ^* −δ _B 'ΔT (26)
If the target rear wheel rudder angle δf ^* and the target rear wheel rudder angle δ _d ^* during deceleration are equal, the control returns to deceleration.

[Front and rear wheel steering control processing]
FIG. 6 is a flowchart showing the flow of front and rear wheel steering control processing executed by the steering controller 3, and each step will be described below.

  In step S1, the target front and rear wheel steering angles during normal control are determined, and the process proceeds to step S2.

  In step S2, it is determined whether the vehicle deceleration A is equal to or greater than a threshold value As. If YES, the process proceeds to step S3. If NO, the process proceeds to step S15.

In step S3, a difference value Δθ ^* between the target front wheel steering angle θ ^* and the equivalent value θ _d ^* of the target front wheel steering angle during deceleration is calculated, and the process proceeds to step S4.

  In step S4, it is determined whether or not the flag F is 2. If YES, the process proceeds to step S8, and if NO, the process proceeds to step S5. Here, the flag F = 2 indicates that the rear wheel neutral slip return control or the deceleration return control is being performed.

In step S5, the deceleration target rear wheel steering angle δ _d ^* is calculated from equation (19), and the process proceeds to step S6.

  In step S6, the flag F is set to 1, and the process proceeds to step S7. Here, the flag F = 1 indicates that the deceleration control is being performed.

In step S7, the front wheel steering actuator 6 and the rear wheel steering actuator 7 are driven based on the target front wheel steering angle θ ^* and the target rear wheel steering angle δf ^*, and the process proceeds to return.

In step S8, the rear wheel steering angle return speed δ _B 'is determined, and the process proceeds to step S8.

In step S9, it determines whether deceleration target rear wheel steering angle [delta] _d ^* is larger than the target rear-wheel steering angle delta] f ^*. If YES, the process proceeds to step S10, and if NO, the process proceeds to step S11.

In step S10, the target rear wheel steering angle Δf ^* is determined from equation (25), and the process proceeds to step S12.

In step S11, the target rear wheel steering angle Δf ^* is determined from equation (26), and the process proceeds to step S12.

In step S12, it determines whether the target rear wheel steering angle delta] f ^* a deceleration target rear wheel steering angle [delta] _d ^* are equal. If YES, the process proceeds to step S13. If NO, the process proceeds to step S14.

  In step S13, the flag F is set to 1, and the process proceeds to step S7.

  In step S14, the flag F is set to 2, and the process proceeds to step S7.

  In step S15, it is determined whether the flag F is 1 or 2. If YES, the process proceeds to step S16, and if NO, the process proceeds to step S23.

In step S16, the rear wheel steering angle return speed δ _A ′ is determined, and the routine proceeds to step S17.

In step S17, it is determined whether the target rear wheel steering angle δ ^* during normal control is larger than the target rear wheel steering angle δf ^* . If YES, the process proceeds to step S18. If NO, the process proceeds to step S19.

In step S18, the target rear wheel steering angle Δf ^* is determined from the equation (23), and the process proceeds to step S20.

In step S19, the target rear wheel steering angle Δf ^* is determined from the equation (24), and the process proceeds to step S20.

In step S20, it is determined whether or not the target rear wheel steering angle δf ^* and the target rear wheel steering angle δ ^* during normal control are equal. If YES, the process proceeds to step S21. If NO, the process proceeds to step S22.

  In step S21, the flag F is set to zero, and the process proceeds to step S7. Here, the flag F = 0 indicates that the normal control is being performed.

  In step S22, the flag F is set to 2, and the process proceeds to step S7.

In step S23, the normal target rear wheel steering angle δ ^* is set as the target rear wheel steering angle δf ^* , and the process proceeds to step S24.

  In step S24, the flag F is set to zero, and the process proceeds to step S7.

[Front and rear wheel steering control operation]
(Normal control)
During traveling other than rapid deceleration, such as steady traveling, the flow proceeds from step S1, step S2, step S15, step S23, step S24, and step S7 in the flowchart of FIG. The angle δ ^* is set as the target rear wheel steering angle δf ^*, and in step S7, the rear wheel steering actuator 7 is driven based on the target rear wheel steering angle δ ^* .

(Control during deceleration)
When the vehicle decelerates rapidly, the flow proceeds from step S1, step S2, step S3, step S4, step S5, step S6, and step S7. That is, in step S5, the determined deceleration target rear wheel steering angle [delta] _d ^* is based on the equation (19), in step S7, based on the deceleration target rear wheel steering angle [delta] _d ^*, the rear wheel steering actuator 7 Is driven.

Therefore, since the rear wheels 14 and 14 are steered to the same phase as the front wheels 11 and 11, the vehicle steer characteristic is suppressed from being oversteered, and the vehicle behavior can be stabilized. Since the target front wheel steering angle θ ^* during the deceleration control is the same as that during the normal control, the neutral deviation of the front wheels 11 does not occur.

In addition, the target rear wheel steering angle θf ^* during deceleration control increases as the vehicle speed V decreases, so the driver suddenly decelerates in the holding state and the front wheel steering angle suddenly increases due to variable gear ratio control. However, it is possible to avoid excessive cutting inward of the turning of the vehicle.

(Rear wheel neutral slip return control)
When the deceleration gradually decreases and approaches to stop, the process proceeds from step S1 → step S2 → step S15 → step S16 → step S17. In step S17, the target rear wheel steering angle δ ^* during normal control is set to the target When it is larger than the rear wheel steering angle δf ^* , the process proceeds to step S18 → step S20 → step S22 → step S7. In step S7, the target rear wheel steering angle δf ^* = δf _i−1 ^* determined in step S18 ^. Based on + δ _A 'ΔT, the rear wheel steering actuator 7 is driven.

On the other hand, if the target rear wheel steering angle δ ^* during normal control is equal to or smaller than the target rear wheel steering angle δf ^* in step S17, the process proceeds to step S19 → step S20 → step S22 → step S7. The rear wheel steering actuator 7 is driven based on the target rear wheel steering angle δf ^* = δf _i-1 ^* −δ _A 'ΔT determined in step S19.

If the target rear wheel steering angle δf ^* is substantially equal to the target rear wheel steering angle δ ^* during normal control during the neutral slip return control, step S1, step S2, step S15, step S16, step S17, The process proceeds from step S18 (step S19) → step S20 → step S21 → step S7. In step S21, since the flag F is set to zero, the control returns to the normal control described above.

Therefore, since the rear wheel neutral slip return control is performed in a state in which the driver at the extremely low speed or at the time of stopping is difficult to notice, the uncomfortable feeling given to the driver can be reduced. Furthermore, since the target rear wheel rudder angle is gradually returned to the target rear wheel rudder angle δ ^* during normal control at δf ^{* at a} constant speed, sudden changes in the target rear wheel rudder angle due to control switching are suppressed.

(Control return control during deceleration)
If sudden deceleration is started again during neutral slip return control, the process proceeds from step S1 → step S2 → step S3 → step S4 → step S8 → step S9. In step S9, the target rear wheel steering angle δ _d during deceleration ^{When *} is larger than the target rear wheel steering angle δf ^* , the process proceeds to step S10 → step S12 → step S14 → step S7. In step S7, the target rear wheel steering angle δf ^* = δf _i determined in step S10. _{Based on -1} ^* + δ _B 'ΔT, the rear wheel steering actuator 7 is driven.

On the other hand, when the target rear wheel steering angle δ _d ^* during deceleration is equal to or smaller than the target rear wheel steering angle δf ^* in step S9, the process proceeds to step S11 → step S12 → step S14 → step S7. The rear wheel steering actuator 7 is driven based on the target rear wheel steering angle δf ^* = δf _i-1 ^* −δ _B 'ΔT determined in step S11.

If the target rear wheel rudder angle δf ^* becomes substantially equal to the target rear wheel rudder angle δ _d ^* during deceleration during the above-described deceleration control return control, step S1 → step S2 → step S3 → step S4 → step S8 → Step S9 → Step S10 (Step S11) → Step S12 → Step S13 → Step S7. In Step S13, since the flag F is set to 1, the process returns to the above-described deceleration control.

Therefore, even when the vehicle suddenly decelerates during the rear wheel neutral slip return control, it is possible to reliably avoid an excessive cut inward of the turning of the vehicle. Furthermore, since the target rear wheel rudder angle is gradually returned to the target rear wheel rudder angle δ _d ^* during deceleration at δf ^{* at a} constant speed, sudden changes in the target rear wheel rudder angle due to control switching are suppressed.

[Rear wheel in-phase control during sudden deceleration]
FIG. 7 is a time chart showing the control action during deceleration of the first embodiment, and shows the vehicle speed V, the front wheel steering angle θ, and the rear wheel steering angle δ when the vehicle is suddenly decelerated in the steering holding state after sudden acceleration.

In the variable gear ratio control, the steering gear ratio is set to be smaller as the vehicle speed V is lower in order to improve the turning performance in the low vehicle speed range. Therefore, when rapid deceleration in the steering hold state with respect to the steering angle theta _str of the holding steering state, the front-wheel steering angle theta increases rapidly. As a result, the vehicle excessively cuts into the inside of the turn (tack-in).

Therefore, in the technology described in Japanese Patent Laid-Open No. 2001-270451, the turning speed at which the vehicle cuts excessively is improved by slowing the change speed of the front wheel steering angle θ during sudden deceleration. However, since a neutral deviation occurs between the steering angle θ _str and the front wheel steering angle θ, it is necessary to return the front wheels to the normal control position when stopping. At this time, although the driver does not operate the steering wheel, the driver receives a steering reaction force accompanying the correction of the neutral deviation, which gives the driver an uncomfortable feeling.

  On the other hand, in the first embodiment, the turning of the vehicle excessively is improved by turning the rear wheel steering angle δ to the same phase as the front wheels while keeping the front wheel steering angle θ at the normal control. At the same time, no neutral deviation occurs in the front wheel steering angle θ, and even if the rear wheel neutral deviation is returned, the steering reaction force is not transmitted to the driver because the steering and the rear wheels are not mechanically connected. In addition, in the first embodiment, when the deceleration decreases after sudden deceleration, that is, when the vehicle speed is sufficiently low, the rear wheel neutral deviation is returned, so that the change in the vehicle behavior due to the returning operation is not noticeable.

Next, the effect will be described.
In the front and rear wheel steering control device of the first embodiment, the following effects can be obtained.

(1) Variable gear ratio control means for increasing the steering gear ratio, which is the ratio of the steering steering angle to the front wheel steering angle as the vehicle speed V increases, and the rear wheel that controls the rear wheel steering angle in accordance with the vehicle speed V and the steering steering angle. And a front and rear wheel steering control device that independently controls the front wheel steering angle and the rear wheel steering angle when the vehicle deceleration A is equal to or greater than a deceleration threshold A _s. Since the steering control controller 3 that executes the deceleration control that steers the vehicle to the same phase as the front wheels 11 and 11 is provided, the vehicle steer characteristics tend to be oversteered without the neutral deviation of the front wheels 11 and 11. The vehicle behavior can be stabilized. Further, since the rear wheels 14 and 14 and the steering wheel 10 are not mechanically connected, even when correcting the rear wheel neutral deviation associated with the control during deceleration, the driver may feel uncomfortable due to the steering reaction force. Absent.

  (2) During the deceleration control, the steering controller 3 increases the rear wheel rudder angle as the vehicle speed V decreases (equation (19)). Therefore, even if the driver decelerates suddenly while maintaining the steering, Excessive cuts can be avoided.

(3) steering controller 3 returns during deceleration control, when the deceleration A of the vehicle is smaller than the deceleration threshold A _s, the wheel steering angle after the corresponding rear wheel steering angle to the normal control Since the rear wheel neutral slip return control is executed, the driver feels uncomfortable by returning the rear wheel neutral slip in a state in which the driver immediately before the stop or after the stop is difficult to notice.

  (4) During the rear wheel neutral slip return control, the steering controller 3 gradually (at a constant speed) returns the rear wheel steering angle to the rear wheel steering angle corresponding to the normal control (Equations (23) and (24)). Therefore, when the control is switched from the rear wheel neutral slip return control to the normal control, it is suppressed that the rear wheel steering angle control amount becomes excessive, and a sudden change in the vehicle behavior can be prevented.

(5) the steering control controller 3, in the control back rear wheel neutral position deviation, when the deceleration A of the vehicle becomes a deceleration threshold A _s or more, corresponding to the deceleration control the rear wheel steering angle Kowakaji Since the control return control at the time of deceleration returning to the corner is executed, even when the vehicle suddenly decelerates during the rear wheel neutral slip return control, it is possible to reliably avoid an excessive cut inward of the vehicle turning.

  (6) The steering controller 3 gradually returns (at a constant speed) the rear wheel steering angle to the rear wheel steering angle corresponding to the deceleration control during the deceleration return control (Expressions (25) and (26)). Therefore, when the control is switched from the deceleration return control to the deceleration control, the rear wheel steering angle control amount is suppressed from being excessive, and a sudden change in the vehicle behavior can be prevented.

(Other examples)
The best mode for carrying out the present invention has been described based on the first embodiment. However, the specific configuration of the present invention is not limited to the first embodiment and does not depart from the gist of the present invention. Any change in the design of the range is included in the present invention.

For example, in the first embodiment, an example in which the gain for determining the target rear wheel steering angle for the deceleration control is obtained with reference to a gain map based on the vehicle speed, but may be obtained from the relationship of the yaw rate.
The present invention can also be applied to a so-called steer-by-wire system in which the steering wheel and the front wheel steering mechanism are mechanically separated.

1 is an overall system diagram of a front and rear wheel steering control device of Embodiment 1. FIG. 4 is a control block diagram of a steering control controller 3. FIG. 3 is a control block diagram of a target value generation unit 31. FIG. 4 is a control block diagram of a target output generation unit 32. FIG. It is a gain map according to the vehicle speed. 3 is a flowchart showing a flow of front and rear wheel steering control processing executed by a steering control controller 3. 3 is a time chart illustrating a control action during deceleration according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering angle sensor 2 Vehicle speed sensor 3 Steering control controller 31 Target value generation part 311 Vehicle model calculation part 312 Target value calculation part 32 Target output generation part 321 Target front and rear wheel steering angle calculation part 322 Target front wheel steering angle difference value calculation part 323 Gain Calculation unit 324 Deceleration rear wheel steering angle calculation unit 325 Deceleration control switching determination unit 4 Front wheel steering controller 5 Rear wheel steering controller 6 Front wheel steering actuator 7 Rear wheel steering actuator 10 Steering wheel 11, 11 Front wheel 12 Front wheel steering mechanism 13 Column shaft 14, 14 Rear wheel 15 Rear wheel steering mechanism 16 Front wheel actual steering angle sensor 17 Rear wheel actual steering angle sensor

Claims (6)

Variable gear ratio control means for increasing the steering gear ratio, which is the ratio of the steering angle to the front wheel rudder angle as the vehicle speed increases;
Rear wheel steering control means for controlling the rear wheel steering angle according to the vehicle speed and the steering steering angle;
With
In the front and rear wheel steering control device for independently controlling the front wheel steering angle and the rear wheel steering angle,
Front / rear wheel steering characterized in that there is provided a decelerating rear wheel steering angle control means for executing a decelerating control to steer the rear wheel to the same phase as the front wheel when the vehicle deceleration is equal to or greater than a deceleration threshold. Control device. In the front and rear wheel steering control device according to claim 1,
The front and rear wheel steering control device is characterized in that the rear wheel steering angle control means at the time of deceleration increases the rear wheel steering angle as the vehicle speed decreases during the control at the time of deceleration. In the front and rear wheel steering control device according to claim 1 or 2,
The rear wheel steering angle control means at the time of deceleration after returning to the rear wheel steering angle corresponding to the rear wheel steering control when the deceleration of the vehicle becomes smaller than the deceleration threshold value during the control at the time of deceleration. A front and rear wheel steering control device that performs wheel neutral slip return control. The front and rear wheel steering control device according to claim 3,
The rear wheel steering angle control means at the time of deceleration is characterized by gradually returning the rear wheel steering angle to the rear wheel steering angle corresponding to the rear wheel steering control during the rear wheel neutral deviation return control. apparatus. In the front and rear wheel steering control device according to claim 3 or 4,
The rear wheel steering angle control means at the time of deceleration is a rear wheel steering angle corresponding to the control at the time of deceleration when the vehicle deceleration becomes equal to or greater than the deceleration threshold during the rear wheel neutral slip return control. A front and rear wheel steering control device that executes control return control during deceleration to return to a wheel steering angle. In the front and rear wheel steering control device according to claim 5,
The front and rear wheel steering control device is characterized in that the rear wheel steering angle control means during deceleration gradually returns the rear wheel steering angle to the rear wheel steering angle corresponding to the control during deceleration during the deceleration control return control.

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